Thermostatic switch



Jan. 29, 1952 H F, HlLD THERMOSTATIC SWITCH Filed Nov. 22 1950 PatentedJan. 29, 1952 THERMOSTATIC SWITCH Henry F. Hild, Merion Park, Pa.,assignor to Proctor Electric Company, Philadelphia, Pa., a corporationof Pennsylvania Application November 22, 1950, Serial No. 197,069

5 Claims. (01. 200-139) The present invention relates to an improvedcontact arrangement for thermostatically operated switches.

Its specific purpose is to provide a contact arrangement that will (a)provide contact wipe during normal cyclic operation, (b) provide asubstantial amount of contact scrubbing during the adjustment of thethermostat at different operating levels, in a situation where thecontacts fail, as by a build-up of an oxide film, the deenergization ofthe device will cause the thermomotive member to cool and in so doingwill institute a substantial amount of contact scrubbing or wipe andthereby act to clear the contacts of such film and reestablish circuitconnections.

The preferred embodiment of the invention is shown in the accompanyingdrawing as an adaptation of the thermostatic control mechanism disclosedand claimed in the pater"- of Joseph W. Myers, No. 2,546,471, issuedMarch 2'7, 1951. As illustrated, the invention is applied to the controlof a device such as a flatiron, but it is to be understood that theinvention is applicable to any use for which it may be suitable.

In the drawing:

Fig. 1 is a longitudinal sectional view of the thermostatic controlmechanism including the switch structure of the present invention;

Fig. 2 is a smaller scale plan view of the mechanism;

Fig. 3 is a partial bottom view of the portion including the novelswitch structure;

Fig. 4 is a partial side view showing the switch contacts and the actionthereof;

Fig. 5 is a similar enlarged view for better illustration of the contactscrubbing action; and Figs. 6 to 9 are perspective views of certainparts of the mechanism.

Referring to the drawings, the thermostatic control mechanism is shownin Fig. 1 in association with a portion of a body In to be heated whichmay be regarded as a portion of the sole plate in an electrically heatedflatiron. The thermostatic control mechanism is constructed andassembled as a unit, the parts of which are carried by an elongate rigidsupport member II which is preferably of inverted channel shape havingdepending side flanges I2 and I3. At

one end of the support member II there is provided a depending hollowsupport element ll which is riveted over at I5 to secure the same to thesupport member. The entire thermostatic control unit is attachable tothe body III by means or a screw I6 passing through the hollow elementI4.

Secured to the lower end of element I4 is a main or primary thermomotiveelement I! which may be in the form of a bimetal strip. The bimetalstrip I1 is disposed so as to be in good heat conductivity relation withthe body I0 adjacent the root portion of said bimetal, receiving agreater portion of its heat from the contact of its root with the bodyI0, and is arranged to flex upward under an increase in temperature.

A compensating thermomotive element I9, which may also be a bimetalstrip, extends from the free end of the main thermomotive strip I'Isubstantially in horizontal alignment therewith. One end of the strip I9is loosely pivotally engaged by the free end of the strip H (see Figs.1, 6 and 7). The cher end of the compensator bimetal I9 is bifurcated toreceive a porcelain button 20, and is arranged to actuate the switchmechanism to be described presently. Intermediate the ends of thecompensating bimetal strip I9 there is provided a suspension fulcrum forsaid strip. As may be seen in Fig. 1, a hollow internally threadedsupport element 2| is mounted on the rigid support member I I. Theelement 21 supports a spindle 22 having a threaded portion 23 threadedlyengaging the element 2|. Below the threaded portion 23 the spindle 22 istapered at 24 and terminates in a pin-like end 25 having an enlargedhead 25. The pin-like portion extends loosely through an aperture 21provided in the bimetal strip I9, thus providing a loose fulcrummounting for the strip l9.

At the upper portion of spindle 22 is provided an arrangement formounting a control knob 28, which includes a factory adjustment element29, as described at length in the aforementioned copending application.A spring member 30, having a bifurcated end for engaging a shoulder 3|on the spindle 22, is riveted at 32 to the elongate member I I and actsto bias the spindle so that any lost motion in the threaded portion 23is taken up in one direction against the corresponding threaded portionin the hollow member 2I.

The mechanism thus far described is substantially similar to the devicedisclosed in the aforementioned copending application. The improvementsprovided by this invention reside in the contact arrangement now to bedescribed.

The switch members which are in substantial horizontal alignment withthe compensating bimetal I9 and the primary bimetal I1 comprise astationary contact 40 fixed to the support memher I I and a movablecontact assembly 4| secured to the support II. The stationary contact 40is electrically isolated from the support I I by means of a porcelainwasher 43 and mica insulating members 44 and 45, and secures a collectortype terminal member 45 to the top of the support by riveting over theend of said contact. The movable contact assembly 41 includes a lever 41having a contact 49 fixed thereto, a flexible connector 49 held betweenthe contact member 49 and the lever 41 (see Fig. 8), and a flat springmember 50 engaging the lever 41 at 51 and urging the same upward. Asshown in Fig. 8, the lever 41 is a relatively stiff or rigid memberwhich includes, besides the contact 48 and the flexible connector 49attached thereto, a hole 52 through which a finger 50a on the spring 50extends (Fig. 1) and a V-shaped fulcrumming portion 53 through which thelever 41 engages the surface of the insulating member 44 at the lowerside of the support member 11. The lever is provided with an extensionfinger 54 for insertion in a cooperative slot 55 in the spring member50. The purpose of this arrangement is to enable the lever 41 to moverelative to the spring member 50 as hereinafter described, while at thesame time the spring member supports and locates the lever.

The flexible connector 49, preferably of high conductivity material suchas silver, is L-shaped and has two holes at its respective ends forattachment below the contact 48 and for attachment to a rivet member 55which is insulated from the support member and connected mechanicallyand electrically to a second terminal member 51. As assembled, thegreater part of the connector lies below and parallel to the springmember 49; however, in the vicinity of the finger 54 the connector islooped to avoid interference with the operation of the contacts.

The spring member 50 is secured between the fixed end of connector 49and a bearing washer 58 by the rivet member 55. The clearance betweenthe finger 50a of the spring member 50 and the cooperating hole 52 ofthe lever member 41 avoids any interference or binding of the memberswhile still providing a rather close fit for transmitting motion betweenthese two members.

Rivet G is insulated from the support member Ii by means of insulatingbushings 59 and 60, made preferably of porcelain, and by mica members44, 45 and iii. The terminal member 51 is held below the riveted end ofmember 56. R'ivet 58 also secures, but is insulated from, a secondcollector type terminal member 62. Terminal members 46 and 51 areconnected in series with the heating element of the flatiron and thesupply line, so that operation of the switch contacts controls thecurrent to said heating element. Terminal 82 connects one end of theheating element to one end of the supply line.

The operation of the primary and compensating thermostatic elements 11and 19 for the control of the heated body through operation of thecontacts 40 and 49 has been explained at length in the aforementionedcopending application. Briefly, increase in temperature of the primarybimetal 11 will cause its free end to flex upward imparting a rockingmovement to the compensating bimetal 19 with corresponding downwardmovement of the movable contact 48. Temperature rise of the compensator18 will cause concave upward flexure and result in a correspondingdecrease in total deflection transmitted to the contact 48.

Consideration will now be given to that part of the operation concerningthe novel contact wipe arrangement, with particular reference to F18 4and 5.

First, cgntact wipe or scrubbing takes place when control knob is isrotated from its "oi!" position, with the fiatiron cold, to one of theon" positions. The position of the thermostat members in their coldstate with the control knob in its of! position is shown in Fig. 1. Itwill be observed that during the movement from of! position theporcelain button 20 at the end of the compensator will be moved upward.The spring member I. will cause a slight clockwise rotation of levermember 41 and a sliding movement of this member at the button 29contacting area and at the area of engagement of the lever fulcrum 54with the mica surface 44. This prevails until engagement is made betweenthe flat face of contact 44 and the arcuate face of stationary contact44. At this instant the lever fulcrum II leaves the mica surface, and asmotion of the button it continues upward, the fist contact 4| slides androtates along the surface of the contact 40. The action of the springmember 54 is to bias the lever 41 upward urging it against the button 20and to cause it to rotate and its contact 48 to slide over thestationary contact 49. Coaction between finger 50a and adjacentshoulders of spring member 50 through hole 52 of lever 41 restrainssideward motion of this lever and causes scrubbing action between thespherical and flat seats of surfaces of the contact members 40 and 44.

A second scrubbing action takes place during normal cyclic opening andclosing of the contacts 49 and 48. It is well known to those skilled inthe art that due to the thermal inertial characteristics of a thermostatand the device being controlled there is an inherent over and undershoot after each opening and closing operation of the contactsrespectively. Thus after the contacts have once engaged, the thermostatsystem continues to lose heat and to decrease in temperature for a shortinterval of time, and during this time the thermostat system continuesto operate in a direction of further contact closure. Similarly oncontact opening, the bimetal system continues to gain heat for a shortperiod thereby effecting greater opening of the contacts before the massbeing heated cools sufficiently for the temperature of the bimetal todecline and effect consequent making of the contacts. It is during theundershoot of the contactmake period of the present thermomotive systemthat scrubbing action between the contacts can be observed, for there isa measure of such action during movement of the bimetal to its coolestposition and a further scrubbing action during heating of this bimetaluntil contact separation is had.

A third and rather important wipe creating condition results from thefailure of the contact surfaces due to oxide build-up thereon. Thiscircumstance may arise during cyclic opening and closing of the contactswhere the level of oxide build-up on the contacts becomes so great thatno circuit will be established between the contacts 49 and 49 eventhough cooling of the thermostat will permit the contacts to engage. Itis during this instant that the thermostat continues to cool andapproach its cold position. This causes an extremely large stroke of theporcelain button II with a large relative movement between the levermember 41 and fixed contact 4| caused by the spring member 59, with aresulting breaking of the film of oxide and reestablishing of theelectrical circuit.

The application and advantages of the novel contact arrangement havebeen described with reference to a fiatiron thermostat. However, it willbe obvious to those skilled in theart that this invention is capable ofvariations and other fields of application than shown herein.

I claim:

1. In an adjustable thermostat control mechanism for controlling theoperation of a heating device at any one of a plurality of temperaturelevels, a fixed contact, a movable rigid lever, a second contact on saidlever engageable with said fixed contact, means providing a surfaceadjacent said lever in fixed relation to said first contact, said leverbeing arranged to engage and to fulcrum on said surface to effectseparation of said contacts, means engaging said lever for moving thesame in response to temperature change and also in response to change bymanual ad justment, and means for locating said lever and for biasingthe same whereby movement of the lever-engaging means results in arelative sliding motion between the movable and fixed contacts when thefulcrum portion of the lever leaves the fixed surface.

2. In an adjustable thermostat control mech-.

anism for controlling the operation of a heating device at any one of aplurality of temperature levels, a fixed contact, a movable rigid lever,a second contact on said lever engageable with said fixed contact, thesurface of one of said contacts being arcuate in profile, meansproviding a surface adjacent said lever in fixed relation to said firstcontact, said lever being arranged to engage and to fulcrum on saidsurface to effect separation of said contacts, means engaging said leverfor moving the same in response to temperature change and also inresponse to change by manual adjustment, and means for locating saidlever and for biasing the same whereby movement of the lever-engagingmeans results in a relative sliding motion between the movable and fixedcontacts when the fulcrum portion of the lever leaves the fixed surface.

3. In an adjustable thermostat control mechanism for controlling theoperation of a heatingdevice at any one of a plurality of temperaturelevels, a fixed contact, a movable rigid lever, a second contact on saidlever engageable with said fixed contact, means providing a surfaceadjacent said lever in fixed relation to said first contact, said leverbeing arranged to engage and to fulcrum on said surface to effectseparation of said contacts, primary and secondary thermostaticelements, the latter being adjustable and engaging said lever for movingthe same in response to temperature change and also in response tochange by manual adjustment, and means for locating said lever and forbiasing the same whereby movement of the secondary ther mostatic elementresults in a relative sliding motion between the movable and fixedcontacts when the fulcrum portion of the lever leaves the fixed surface.

4. In an adjustable thermostat control mechanism for controlling theoperation of a heating device at any one of a plurality of temperaturelevels, a fixed contact, a movable rigid lever, a second contact on saidlever engageable with said fixed contact, means providing a surface adjacent said lever in fixed relation to said first contact, said leverbeing arranged to engage and to fulcrum on said surface to effectseparation of said contacts, means engaging said lever for moving thesame in response to temperature change and also in response to change bymanual adjustment, and a spring member arranged to locate and bias saidlever whereby movement of the lever-engaging means results in a relativesliding motion between the movable and fixed contacts when the fulcrumportion of the lever leaves the fixed surface.

5. In a thermostatic switch, a fixed contact, means providing a surfaceadjacent said contact and in fixed relation thereto, a rigid leverhaving a fulcrum portion engageable with said surface and also movabletherefrom, a contact on said lever engageable with said fixed contact, aspring member pivotally engaging said lever and urging it in a directionto close said contacts, and a thermostatic element engaging said leverand serving to control the movement thereof, the movement of said leverin opposite directions causing the contact thereon to slide on saidfixed contact.

HENRY Fl HILD.

No references cited.

